The removal of H2S from various streams is a problem that has challenged many workers in many industries. One such industry concerns streams and quantities of molten sulfur. When sulfur is produced in a refinery it is in a molten or liquid form that is typically stored in pits in the ground or possibly in insulated storage tanks. The reaction of the sulfur with hydrocarbon impurities present in the material and the decomposition of sulfhydryl compounds—typically with the general formula H—S—(S)x—S—H—which are also present in the sulfur form hydrogen sulfide. The hydrogen sulfide in turn is a safety and odor problem. The problem may occur at the refinery in their storage pits/tanks or in vessels such as rail cars and tank trucks, which transport the sulfur from the refinery. It is desirable to prevent the evolution of hydrogen sulfide from molten sulfur during storage and/or distribution.
The presence of H2S presents many environmental and safety hazards. Hydrogen sulfide is highly flammable, toxic when inhaled, and strongly irritates the eyes and other mucous membranes. Flaring of gas that contains H2S does not solve the problem for gas streams because, unless the H2S is removed prior to flaring, the combustion products will contain unacceptable amounts of pollutants, such as sulfur dioxide (SO2)—a component of “acid rain.”
Hydrogen sulfide has an offensive odor, and natural gas containing H2S often is called “sour” gas. Treatments to reduce or remove H2S from substrates often are called “sweetening” treatments. The agent that is used to remove or reduce H2S levels sometimes is called a “scavenging” agent. The prevention of H2S evolution from molten sulfur is only one example of where H2S level inhibition, reduction or removal must be performed.
The problem of removing or reducing H2S from molten sulfur has been solved in many different ways in the past. Oxidizers such as sodium or calcium hypochlorite or hypobromite have been used as scavengers in liquid sulfur. Air has also been used as an oxidizer to convert H2S to elemental sulfur.
Other approaches involve intentionally promoting the evolution or degassing of H2S from the molten sulfur. That is, various additives are used to intentionally cause sulfhydryl species such as H—S—(S)x—S—H to decompose. The H2S formed is then swept away to a vapor recovery system. Once these materials are decomposed, the sulfur is left with reduced potential to form more H2S and may be relatively safer to transport. Typical compounds used in such methods contain nitrogen.
U.S. Pat. No. 5,552,060 describes a method for scavenging H2S from aqueous and hydrocarbon substrates using an epoxide. Preferred epoxides are styrene oxide, 1,3-butadiene diepoxide, and cyclohexene oxide.
A continuing need exists for alternative processes and compositions to inhibit H2S evolving from molten sulfur. It would be desirable if compositions and methods could be devised to aid and improve the ability to accomplish this task and not have any disadvantageous impact on the end uses of the sulfur.